The existing threads about bushes looked to be pretty old, this is my first post here so I hope I'm not causing a problem by starting a new topic. Hopefully my questions are different enough to justify...

I built my locost using the book front suspension arm design for the chassis side: 25mm diameter 36mm long, 21mm ID bush tubes,
My brackets are non-book, I used 2"x1/8" square tube cut to size, drilled through for a 3/8" bolt, then one side opened to shape. So my inside bracket width is 45mm vs 36mm in the book (sorry for the mixed units).

I turned my own bushes from delrin to fit - 21mm OD inside with a 25mm x 3mm shoulder. 16g crush tubes to fit the 1/ 3/4" brackets. Crush tubes are cut from 16g 1/2" tube (for a 3/8" inside bolt).

After about 1000km the shoulders crumbled on my homemade bushes . The handling started to be a bit squirmy under braking.

I'm running two experiments now:

I purchased a bushing set supposedly for the spitfire, but not the metalastic ones - these are solid with a 3mm shoulder. They're the same width of the metalastic bushes at 36/37mm, but the metalastic bushes don't have that shoulder. What am I missing, how could they fit the spitfire?

In any case they fit my bush tubes and brackets well but I had to re-use my own longer 45mm crush tubes. This is experiment 1. The top arms are far easier to change in place than the bottoms! And I have 4 spare sets if needed.

On the bottom I used some compliant 20mm hollow polyurethane tube. I cut it into 37mm length pieces, then opened the inside to just under 1/2" for my crush tubes. They fit snugly using a C-clamp, the crush tube slightly expanding the polyurethan to a snug bush tube fit (mine are about 21.5mm ID). 1/2" x 1/8" solid nylon washers fit on the crush tube ends to fill my brackets. Experiment 2, I'll be watching to see how those nylon washers hold up with use. I might try 1/2"ID x 1/8" steel washers if they fail. I'm guessing the polyurethane will be ok since it's well supported all around.

Free movement was snug with no binding after assembly. 300km or so now and they're holding up so far, handling seems firm, no squeaking or obvious damage.

If either experiment fails my next attempt will probably be with the metalastic bushes, and some 3/8" x 1/8 stainless washers on either end to keep them in place on the 3/8" bolts.

Any guidance / criticism / warnings / or BTDT stories would be appreciated!

Do you have any pictures you can share?

How it looks on the car and the parts you have?

Sure, here's what I have, thanks for asking.

Summarizing (in imperial 'cause it's a bit easier for me), the book and metalastic bushes measurements:
bush tube 1.4", crush tube, bush, and bracket width 1.5" for a snug fit.

On mine, bush tube 1.4", bracket and crush tube 1 3/4", allowing a 1/8" shoulder each end of the bush - perhaps my problem?

Here's what a bought. comes with a 1.5" crush tube, the 1/8 shoulder + my 1 3/4" crush tube work well for me.

spitifire bushes?
How do they work in spitfire control arms?

Here's my top, with 1 3/4" crush tube in my brackets:

spitfire? bushes


And my bottoms, with 20mm polyurethane inside, 1 3/4" crush tube, and 1/2" x 1/8" thick white nylon washers:

poly + nylon bush

Maybe steel washers as spacers would be better?

hmm, well your car looks to be designed for press in Spitfire metalastic bushes, not the poly top hat type you show as they are much bigger.

I would just get some Spitfire ones, they can't be expensive but you'll need the use of a press to change them out.



That above is completely wrong and only jamming your suspension, the metal centre of the bush (the tube) needs to be clamped and the outer part of the arm free to move i.e not touching anything. At worse you are just flexing the suspension arms and you will make them snap at a weld with interesting results. I also notice that the nut is not cotter pinned or Nylocks. I hope they are at least 10.8 grade too.

[Edited on 20/9/24 by Mr Whippy]

quote:

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Originally posted by Mr Whippy
hmm, well your car looks to be designed for press in Spitfire metalastic bushes, not the poly top hat type you show as they are much bigger.

I would just get some Spitfire ones, they can't be expensive but you'll need the use of a press to change them out.


That above is completely wrong and only jamming your suspension, the metal centre of the bush (the tube) needs to be clamped and the outer part of the arm free to move i.e not touching anything. At worse you are just flexing the suspension arms and you will make them snap at a weld with interesting results. I also notice that the nut is not cotter pinned or Nylocks. I hope they are at least 10.8 grade too.

[Edited on 20/9/24 by Mr Whippy]

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re-reading your original post,
firstly, I have to wonder where your car has done 1,000km + 300km? has it passed an IVA, or even an MOT? or is it a track car?
secondly avoid stainless on suspension

[Edited on 20/9/24 by gremlin1234]

You might have missed the measurements, the brackets are 1.75" inside. The bush tubes are 1.4" (as per the book). The spitfire ones are 1.5"
The distance tubes are 1.75" and clamped tight. The a arms move freely on the bushes when installed and tightened in the brackets, no binding or slop.

Those are indeed 10.8 bolts, the shank spans the bracket. The nuts are flanged interference thread lock nuts (all metal, no nylon, can be reused but a PITA to get off and on).

Really my first question is out of interest - how do those commercial top hat bushes work in a spitfire? I can't figure out how they would fit the brackets and the a-arms, what am I missing?

My main question is why do "performance" bushes tend to be top hat style? It looked like mine failed because the a-arm bush tubes put fore/aft pressure on the flanges while driving and cut into the flanges. The bushes shouldn't be tight enough in the tubes to stop that force or the suspension would bind, right? Perhaps bush tubes should be more chamfered? Or my delrin just wasn't hard enough?

The metalastic bushes are my fallback plan. My hesitation is the 1.5" crush tube need 3/8" x 1/8" washers to fill my brackets. Using a 1/2" crush tube with 1/2" shoulder washers feels stronger to me. I also read the newer (china sourced?) ones fit 10mm while my bolts are 3/8", I don't know which I'd get over here and re-drilling the brackets is not an option.

quote:

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Originally posted by MikeP001
Really my first question is out of interest - how do those commercial top hat bushes work in a spitfire? I can't figure out how they would fit the brackets and the a-arms, what am I missing?

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I'm in Canada, locost finished, inspected, and licensed early this spring just after the snow melted... 1700km so far on public roads, this and the failure of a brand new clutch master have been the only issues so far.

Maybe. Where are trunnion bushes used? I thought they were solid brass or something, like for the kingpin.

This is what I used: https://www.ebay.ca/itm/160905794253
Same here in case they're gone from ebay: https://bpnorthwest.com/triumph/a-arm-bushing-set-poly-spitfire-gt6/
The description does say a-arms.

I wonder if I had my original bushes too tight around the crush tube forcing them to be stationary while the suspension moved? That might cause the bush tubes to cut/wear the top hat shoulders.

The top hat bushes should not be touching anything on the chassis bracket, they should move only with the arm. Only the crush tube should be stationary and rotate within the bush. Looking at you picture with the large nylon washers you are crushing everything and that is clearly wrong. On the ones using metalastic bushes, its the same deal but did you tighten the bolts only once the car was on the ground? ideally with the driver sitting in it? otherwise they will wear very very quickly.

Please use correct bolts and locknuts. Quite a worrying set up so far from the pictures. I've had a wishbone snap at a weld due to a seized bush (production car) and you get no warning at all. Next thing the car is flying across the road, I nearly had a head on with a Golf that time.

I may not understand what you're suggesting...

There's 0.1" clearance for the bushes in the bracket: 1.75" crush tube. 1.4" bush tube + 0.125 shoulder * 2 = 1.65".
Crush tubes are clamped tight and the a-arms move freely in the brackets with no slop. The nylon washers are not crushed tight.


The bolts are 10.8 with the shank supported in the bracket. The nuts were suggested by the fastener vendor: interference thread lock nuts. Similar to nylocs but reusable. I was skeptical too but they in fact have more resistance to loosening than nylocs.

There are no metalastic bushes in my suspension, if you mean the ones on the top those are spitfire solid bushes (product linked above) with shoulders, I added a 1.75" distance tube (same clearances). They're free moving.

Am I missing something?

I'm pretty certain now I had my original bushings too tight on the crush tubes and too loose in the bush tube. Clearly they were turning in the tube and wearing the shoulders. I should be good with the new approach, thanks for the chat/questions to help me think it through.

I found some pictures showing the metalastic bushes sit proud of either side of the spitfire control arms. I can see how the ones with shoulders would fit there.

(edit, I missed the metalastic bush question and added some addln detail).

[Edited on 22/9/24 by MikeP001]